Viral gastroenteritis is an intestinal infection characterized by stomach cramps, nausea, watery diarrhea, or vomiting, and sometimes fever.

The most common way to develop viral gastroenteritis is commonly known as the stomach flu, is through contact with an infected person, or by ingesting contaminated food or water. If you don’t have any other health problems, you’ll probably recover without complications. However, for infants, older adults, and people with compromised immune systems, viral gastroenteritis can be deadly.

In addition to avoiding food and water that may be contaminated, your best defense is frequent and thorough handwashing.

Symptoms

Although commonly called the stomach flu, gastroenteritis is not the same as influenza. The real flu (influenza) only affects the respiratory system, that is, the nose, throat and lungs. On the other hand, gastroenteritis attacks the intestines, and produces signs and symptoms such as the following:

• watery diarrhea usually without blood (bloody diarrhea usually means you have a different, more serious infection);
• abdominal pain and cramps;
• nausea, vomiting, or both;
• occasional headaches or muscle aches;
• low-grade fever

Depending on the cause, symptoms of viral gastroenteritis can appear within one to three days after you get the infection and can range from mild to severe. Symptoms usually last a day or two, but can sometimes persist for up to 10 days.

When you should see a doctor

You can call your doctor if you are an adult and you are feeling:

• You cannot keep liquids down in your stomach for 24 hours
• You have had vomiting for more than two days
• You have bloody vomit
• You are dehydrated: Signs of dehydration include being extremely thirsty, having a dry mouth, bright yellow urine, little or no urine, and feeling severely weak, dizzy, or lightheaded
• You see blood in the stool
• You have a fever above 104°F (40°C)

In the case of babies and children

See your doctor right away if your child:

• Has a fever of 102ºF (38.9ºC) or higher
• Seems lethargic or very irritable
• You feel a lot of discomfort or pain
• You have bloody diarrhea
• He appears dehydrated; watch for signs of dehydration in sick infants and children by comparing the amount of fluid they drink and urinate to the amount that is normal for them

If you have a baby, remember that while spitting up may be an everyday occurrence for him, vomiting is not. Babies vomit for a number of reasons, many of which may need medical attention.

Call your baby’s doctor right away if:

• You have vomiting that lasts for more than several hours
• No wet diaper after six hours
• You have bloody stools or severe diarrhea
• You have a sunken soft spot (fontanel) on the top of your head
• Has a dry mouth or cries without tears
• Sleepy, drowsy, or unresponsive

The stomach, small intestine, and large intestine (colon) are part of the digestive tract, which processes the food you eat. 

Causes

You’re likely to get viral gastroenteritis from eating contaminated food or water, or from sharing utensils, towels, or food with someone who’s infected.

There are several viruses that can cause gastroenteritis, such as:

• Norovirus. Norovirus, the most common cause of foodborne illness worldwide, affects both children and adults. Norovirus infection can invade families and communities. Its spread is especially likely among people who are in confined spaces. In most cases, you come into contact with the virus through contaminated food or water, although person-to-person transmission is also possible.
• Rotavirus. Worldwide, this is the most common cause of viral gastroenteritis in children, who usually contract the infection by putting fingers or other objects contaminated with the virus in their mouths. The infection is more serious in infants and young children. Adults infected with rotavirus may not have symptoms but can still spread the disease, which is especially concerning in institutional settings because infected adults can unknowingly spread the virus to others. In some countries, such as the United States, a vaccine against viral gastroenteritis is available and appears to be effective in preventing infection.

Some shellfish, especially raw or undercooked oysters, can also poison you. Although contaminated water is a cause of viral diarrhea, in many cases the viruses travel through the fecal-oral route; that is, a person infected with the virus does not wash their hands after going to the bathroom and then handles the food they eat.

Risk factors

Gastroenteritis is present throughout the world and affects all people regardless of age, race or background.

People who may be more prone to gastroenteritis are the following:

• Small children. Children in child care centers or attending elementary schools may be particularly vulnerable because a child’s immune system is slow to develop.
• Older adults. The immune system of adults tends to be less efficient at older ages. Older adults in nursing homes are especially vulnerable because their immune systems are weakened and because they live in close contact with others who can spread germs.
• Children of school age, religious or people who live in student residences. Any place where groups of people gather in closed environments can be a transmission environment for intestinal infections.
• Anyone who has a weakened immune system. You are especially at risk if your resistance to infection is low; for example, if your immune system is suppressed by HIV/AIDS, chemotherapy, or another illness.